OpenRocket & Thrustcurve vs. Estes Altitude

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markg

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I drew up an Estes Humdinger (https://www.estesrockets.com/007225-humdingertm) as best I could in OpenRocket and ran the simulation for all the recommended motors. I get a max apogee of 434 ft. I also put the rocket into thrustcurve.org and got similar numbers (https://www.thrustcurve.org/motorguide.jsp?rocket=4482).

Estes says it can fly up to 1100 ft - which number should I believe? Split the difference maybe?

We just got the rocket so I haven't flown it yet, though will probably get it up this weekend.

cheers - mark
 
Estes altitudes are, at best, optimistic based on a perfect world and their motor actually being within spec. Like any other vendor, they're in the propaganda market as much as the rocket market. :D

That said, there are lots of things in OR that will have an effect on your altitude. Check fin cross section, paint surface on EVERY item (click the 'set for all' to make things easier), diameter discontinuity, altitude of the launch field, temp and air density, etc. You can set your parameters to your LAT and LONG and your base altitude and save so that every sim you run is from your field.

Comparing OR sims to actual rockets flights, I find OR to be a better indicator of what I'll get based on data from actual flights and altimeter data for LPR, IF and only IF I've done my part and gotten the weight and balance right in OR. For most all of my MPR and HPR rocket flights, OR underestimated altitude by about 5%.
 
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That said, Estes' estimates are typically not THAT optimistic. They are based on minimal glue and such.

But in this particular case, I have to wonder - a model that size to 1100 feet on an A seems pretty optimistic to me. A smaller model (shorter) with similar fins - the tried and true Gnome - is showing an estimated altitude of up to 800 feet. Even that seems a little optimistic to me.
 
Looks like the NAR record for an A engine is around 300m/984ft, so I'm going to guess that Estes did a copy/paste job on this description and the altitude will end up closer to what I found with the OR/thrustcurve. I'll see how it goes when I try and fly it this weekend.

cheers - mark
 
There can be typos in the Estes catalogs too. A couple of years back I went through a catalog in detail and found maybe half a dozen obvious errors in dimensions, mass and altitude numbers.

Based on competition experience, with 4 fins and that much wetted area, there is no way that design will ever approach 1100' even with a mirror finish and a piston launcher.
 
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